Modulation system



April 1958 h. R. JOHNSON ETA]. 2,830,272

MODULATION SYSTEM Filed April 19, 1954 SOURCE OF BIAS mm HO /W53 61 i/V/V )4, 41/44 7:95

24" VOlJ'AGE ArroPM-XJ United States Patent 2,830,272 r I MODULATION SYSTEM Robert R. Johnson, San Carlos, and Glenn A. Walters,

Atherton, Califl, assignors, by mesne assignments, to Textron'lnm, Providence, R. I., a corporation of Rhode Island V Application April 19, 1954, set-alive. 423,913 I ,7

5 Claims. c1. 332-59 This invention relates to modulation systems and more particularly to a system for producing a'regu'lat'ed, filtered direct current potential which may be modulated.

'It'is common practice in the prior art to employ a regulated'direct current power supply. Such circuits normally include a rectifier tube, a passive filter network, and one or more voltage regulator utbes. The present invention contemplates the production of a filtered, regulated D. C. potential, but principally a D. C. potential which may be modulated in accordance with intelligence.

It is therefore a primary object of theinvention to provide a novel power supply.

Another object of the invention'is to provide a regulated, filtered D. C. potential which may be modulated.

Still another object of the invention is to provide 'a power supply which is capable of beingmodulated from practically zero outputtothe maximum possible output.

A further object of the invention is to provide a'unique Briefly the preferred embodiment utilizes a series volt age regulator tube in conjunction with a degenerative feed-back loop to provide a regulated voltage substantially free of hum. Provision is made for inserting a modulation signal in order to modulate the resultant filtered and regulated output potential.

Referring now to the drawing, reference numeral 10 designates a controlled resistive device which serves as a series voltage dropping or regulator tube. Reference numerals 11 and 12 designate amplifier control devices, which serve as a cathode follower and a D. C. amplifier, respectively. The devices 10, 11, and 12 have been shown for purposes of illustration as triode vacuum tubes including the conventional anode, cathode, and control grid elements as indicated in the drawing. An input voltage from an unfiltered rectifier power supply (not shown) is applied with the positive and negative polarities at terminals 13 and 14 respectively. A conventional filter capacitor 15 is shunted across the input terminals in order to reduce the ham in the output of the unfiltered rectifier power supply. The potential at terminal 13 is applied to the anode of tube 10 and the cathode of the latter is connected to an output terminal 16. connected to a second output terminal 17.

A potential divider comprising resistors 18, 19 is shunted across output terminals 16, 17 as shown. The control grid of tube 12 is energized from the junction of resistors 18 and 19, the resistances of which are chosen to provide the desired grid potential. It will be noted that the control grid of tube 12 is connected to the potential divider through the intermediary of a coil 20, which constitutes the secondary winding of a transformer 21.

Terminal 14 is 2,830,272 Patented Apr. 8, 1958 Transformer 21 has a primary winding 22 to which a modulating signal may be applied. An additionaltransformer winding 23 connects the cathode of tube 12 to a source of bias or reference voltage 24. The primary winding 22 is arranged to induce a voltage inboth of'windings 20 and 23. The latter windings are conected so that the polarities applied to the cathode and control grid of tube 12 are the same for a given instantaneous polarity of the primary winding 22. The anode of tube 12 is connected through ,a resistor 25 to the control grid of tube 10. Tube 11 has its anode connected to the plate of tube 10, its cathode connected to the control grid of tube 10, and its control grid connected to the anode of tube 12. A plateload resistor 26 is included in the anode supply circuitoftube12. i p

Referring now to the operation of the circuit illustrated, tube 10 serves to regulate the output potential appearing at terminals 16', 17. Any variation of this potential will be applied to the control grid of tube '12 by virtue of the voltage divider comprising resistors 18 and 19. ltcan be seen'that a degenerative voltage feed-back loop including resistors 18, 19 and tube 12 is provided for potential 'variations appearing at the cathode of tube 10. Therefore it the potential at terminal, 16 should become more positive, for example, the conductivity of tube 12 will increase and a more negative potential will be applied to the control grid of tube 10, thereby'increasing the resistanceand voltage drop of tube 10 anddecreasing the potential at terminal 16 to counteract the voltage rise.

It can be seen that any hum potential which reduced by the degenerative actionjust described. The 'output voltage at terminals 16, 17 may be modulated in accordance with intelligence or other types of control informationapplied 'tO/lhfi terminals of'coil 22.

Linear modulation of the output'voltageis accomplished byinducing a voltage in coil 23 in the cathode lead of tube 12. A portion of the modulation is applied through coil 2ll.to the control grid of tube 12 in series with the feed-back voltage" across resistor 19. The control grid of tube 12 is driven in the same direction as the cathode, but to a lesser degree. The potential applied to the control grid thereby opposes the change in impedance of tube 12 caused by the change in the potential of the cathode. This action reduces distortion caused by non-linearity in the operation of tube 12 and allows linear modulation of the output potetnial at terminals 16, 17 down to nearly zero volts.

The changes in input voltages at the cathode and grid of tube 12 cause the plate potential of this tube to vary accordingly. These potential variations are applied to the control grid of tube 11 and appear at the cathode of the latter by virtue of the cathode follower operation, thereby varying the potential on the control grid of tube 10. The impedance of tube 10 thus varies in accordance with the signal applied to coil 22 and causes modulation of the potential at terminals 16, 17.

Cathode follower of tube 11 provides a relatively low impedance path for grid current through tube 10 and thus allows the grid of tube 10 to be driven positive with respect to the cathode. In this manner substantially modulation of output potential may be accomplished with lower input potentials at terminals 13, 14.

While a preferred embodiment has been shown and described, many modifications will appear evident to those skilled in the art without departing from the essential concepts of the invention. The above embodiment is therefore to be considered as illustrative of the invention rather than restrictive, and the scope of the invention is terminals, a discharge device having at least an anode, a cathode and a control grid, means connecting the coninterpretation of the follow- I trol grid of said discharge device to said potential divider, 1

means coupling the anode of said discharge device to the control grid of said voltage dropping device, and means for applyinga modulating signaltothe cathode and control grid of said discharge device, said last named means comprising a transformer having a primarywinding to which modulation is applied and a pair of ,windings connected to said cathode and control grid, respectively, said pair of windings being arranged to drive said cathode and control grid in cophasal relationship.

2. The invention of claim 1', further including a source of cathode bias coupled to the cathode of said discharge device.

3. A modulated powerlsupply comprising a pair of input terminals, a pair of corresponding output terminals,

a voltage dropping device having at least an anode, a cathode and a control grid, means connecting said anode and cathode to a corresponding input and output terminal, respectively, a potential divider shunted across said output terminals, a discharge device having at least an anode, a cathode and a control grid, means connecting the ,control grid of said discharge device to said potential divider, means coupling the anode of said discharge device to the control grid of said voltage dropping device, said coupling means including a cathode follower circuit, comprising a second discharge device having an anode, a cathode and a control grid, the control grid of said second discharge device being connected to the anode of said first discharge device,,the cathode of said second discharge device being connected to the grid of said voltage dropping device, the anode of said second discharge device being connected to a source of anode potential; and means for applying a modulating signal to the cathode of said first discharge device. t t

4. A modulated power supply comprising a pair of input terminals, a pair of corresponding output terminals, a voltage dropping device having at least an anode, a cathode and a control grid, means connecting said anode and cathode to a corresponding input and output terminal, respectively, a potential divider-shunted across said output terminals, a discharge device having at least an anode, a cathode and a control grid, means connecting the control grid of said discharge device to said potential divider, means vcoupling the anode of said discharge device to the control grid of said voltage dropping device, a source of signals variable in accordance with intelligence, connection means for coupling said source to said discharge device and applying said signals simultaneously to the cathode and control grid of said discharge device, said connection means being arranged to drive the cathode and control grid of said discharge device in cophasal relationship.

and an output circuit, a controlled voltage dropping device connected between said input and output circuits, a discharge ,device having a plurality of electrodes and connected between said voltage dropping device and said output circuit, said discharge device being responsive to changes of outputof said power supply for controlling said voltage dropping device to oppose said changes, an independent source of modulating signals variable in accordance with intelligence, circuit means connecting said source to at least two electrodes of said discharge device and being arranged to drive said two electrodes in such phase relationship thatthe linear plate current excursion of said discharge device is maximized, said output circuit having circuit constants such that the output circuit is responsive to instantaneous values of said modulation signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,407,458 Spielman Sept. 10, 1946 2,463,275 Henderson Mar. 1, 1949 2,499,423 Selinger n Mar. 7, 1950 2,643,359 Shenk et al June 23, 1953 2,752,555 Light June 26, 1956 5. A modulated power supply having an input circuit 

